Numerous substances have heretofore been known as drugs which act on the circulatory system. Among these, a variety of substances have been developed as antihypertensive drugs.
Of such drugs as employed as circulatory drugs, .alpha..sub.1 -blockers are accompanied by the drawback that they generally have side effects such as orthostatic disorder and reflex tachycardia, tend to induce orthostatic hypotension especially when administered to aged people and hence require attention.
As drugs having less tendency of inducing such side effects of .alpha..sub.1 -blockers, on the other hand, certain drugs having both anti-serotonin action and anti-.alpha..sub.1 action have been developed as drugs effective for senile hypertension and the like. However, these drugs may not be able to exhibit, for example, sufficient hypotensive action in some instances, and their side effects to the central nervous system such as drowsiness and sedative action have posed problems.